Figure
1. Mercy
Corps energy use.
Inside this nonprofit’s new headquarters in Portland, variable refrigerant flow teamed with zonal heat exchange, 100% DOAS, daylighting, CO2sensors, and more to deliver comfort while bringing actual energy usage in under the design target of $0.83 per year.
Headquartered in Portland, OR, for 30 years, Mercy Corps had outgrown its six leased headquarters buildings by 2005 and purchased the historic, 42,000-sq-ft 1892 Packer-Scott building to house its growing staff of unique professionals. Early in 2006, Mercy Corps sat down with its Portland design partners - THA Architecture Inc. and Glumac Engineering, Inc. - to forge plans for its new headquarters building. This consisted of renovating the historic building and creating a large new addition, resulting in a combined area of 82,000 sq ft and finally bringing all Mercy Corps employees together in a single location.
STRIVING FOR LEED® PLATINUM: FOCUS ON ENERGY PERFORMANCE
The building was originally designed for a LEED® Gold rating, but the design team discovered that it was meeting Platinum certification levels and needed a different metric for the building’s new sustainability goals. The team looked to the Living Building Institute’s Living Building Challenge to provide these guidelines. Although the team did not submit for Living Building Challenge certification, the guidelines became an important tool and narrowed the focus to the further reduction of energy and water use.The goal of achieving LEED Platinum focused primarily on energy performance as the building’s urban location, the use of green building materials, and other sustainable design features guaranteed points in other categories. The Performance Rating Method (PRM), as defined in Appendix G of ASHRAE 90.1-2004, was the standard for energy analysis. The design incorporated many energy-efficiency measures (EEMs) that were analyzed throughout the design process, including a variable refrigerant flow (VRF) HVAC system, 100% dedicated outdoor air system (DOAS), carbon dioxide sensors, daylighting, improved envelope insulation, energy-efficient windows, and a planned 80-kW photovoltaic (PV) array.
Since the Mercy Corps headquarters project is partial building renovation and partial new construction, we averaged the New Construction and Existing Building point thresholds for each energy and atmosphere credit to provide new point thresholds. Each threshold is adjusted to 3.6 percentage points less than the New Construction thresholds (e.g. the first point starts at 6.9% instead of 10.5%).
Using LEED and ASHRAE 90.1 rules, energy cost-saving goals were outlined for the building. Without renewables, the budget baseline was calculated to be $37,350 per year or 35%. With the addition of an 80-kW PV array, the building should save an additional $5,000, increasing the total energy cost savings to $42,000 or 40%. Overall, the building was designed to save 136 tons of CO2annually over the ASHRAE baseline.
SELECTING A VRF SYSTEM TO MAXIMIZE ENERGY PERFORMANCE
To reach LEED Platinum, the team had to find a highly efficient HVAC system. The team considered many options, including packaged gas/electric rooftop VAV systems, low-temperature central VAV systems, and VRF fancoil systems.Glumac recommended the VRF zoning system from Mitsubishi Electric Cooling and Heating Solutions, Suwanee, GA, for many reasons. The design team cited simplification through the packaged zone design, quiet fancoils, expansion to accommodate new zones, the advantages of demand-based ventilation, and a relatively moderate cost.
Table
1. Energy
metric for Mercy Corps headquarters.
MERCY CORPS MECHANICAL SYSTEM: ZONAL EXCHANGE
Zonal heat exchange was available for space loads up to 20 tons of cooling, but with careful layout, the systems were provided with cooling diversity up to 25 to 30 tons. The Mercy Corps building is half existing building renovation on the west and half new building addition on the east separated by an open circulation, egress stairs, and elevator shafts. The circulation splits the building into an east-west orientation providing a natural division for the building systems.Looking at a zonal heat exchange system from an energy-savings standpoint, Glumac tried to design the system to distribute loads between internal zones and external facades. The internal heat gains at Mercy Corps were generally from data closets, isolated conference rooms, and a few separate office spaces. These internal loads were not great enough to take any significant diversity in the overall heating loads for the building, but they do provide the interior/exterior heat exchange that results in electrical energy savings.
The more significant impact for heat exchange energy savings has come from the orientation of the building facades and the layout of heat exchange systems. Ideally, all four facades would be incorporated into a single system, but the building was divided into east and west zones due to the circulation layout. The best opportunity for exterior heat exchange comes from the radiant gains on south-facing spaces and the system connection to the north-facing zones. The Portland climate is generally heating dominated, but a good portion of the year has moderate exterior conditions that allow for this perimeter zonal exchange.
CONTROLLING COMFORT LEVELS IN THE WORKSPACE
Prior to moving to its new headquarters, Mercy Corps’ offices were dispersed across a number of buildings. Facility maintenance was difficult and comfortable working environments were hard to arrange. One of the key project goals was to simplify the facility maintenance and allow for a greater level of comfort in the workspace.Off-the-shelf solutions for comfort and control of the VRF system were ideally suited to the building. Variable rates of air delivery from the concealed fancoils allow for better comfort than a typical fancoil system, especially in the open-office environments where a single thermostat can be used to control the entire space. In closed-office environments where one thermostat controls the temperature of multiple occupants, the control system is limited. But by designing many of the individual offices in the building interior, the load variation was minimized. The VRF zoning control system internally maximizes comfort and energy savings, leaving the building engineer with less maintenance and load shedding concerns.
In parallel with the VRF fancoil system, we provided a DOAS to better respond to the building ventilation needs. We sized the DOAS to provide 30% greater airflow than the ASHRAE 62.1 requirements and minimized ventilation as necessary with CO2sensors in all occupied areas.
Rooftop gas-fired units with heat recovery wheels provide variable ventilation delivery rates through VAV terminal units. The terminal units serve ventilation zones that are separated by schedule and occupancy type. High-density zones such as conference rooms are provided with dedicated VAV terminal units and CO2sensors. A parallel DOAS was provided to also allow for economizer air delivery separate from the distributed fancoils.
In Portland, there are more than 1,300 occupied hours a year when outside air conditions are favorable for economizer cooling, enough to be written into the energy-code requirements for the state. A code exception allows for heat exchange systems to be exempt from the economizer requirements, but the Mercy Corps systems allow for both. The parallel ventilation system not only allows for free cooling but creates a simplified sequence of control for the morning warm-up. Prior to building occupancy and VRF system start-up, the DOAS is converted to a recirculation air system and uses the cost-effective natural gas to warm up the building from the overnight set-back temperatures. In the same manner, a nighttime flush sequence is simplified over the summer months. We chose parallel DOAS over series DOAS for the ease of sequencing.
Unlike a typical decoupled ventilation system where the latent and sensible loads are satisfied by the central system and purely sensible loads are satisfied by the distributed system, the VRF fancoils likely provide some level of latent cooling. The cooling surfaces within the fancoil are not able to be controlled by the system to temperatures above the space dewpoint, thus allowing space relative humidity to be ignored as a control point; however, all cooling surfaces within the building require means of condensate removal.
EEMS DEFINED
The systems design incorporated many EEMs that were analyzed throughout the design process for capital cost, energy savings, energy cost savings, payback and carbon footprint (Table 1). These EEMs included in the energy metric boil down to:- A variety of HVAC systems
- DOAS
control schemes and exhaust air heat recovery
- Daylighting control zones
- Electrical
lighting levels
- Improved envelope
insulation including increased insulation from a green roof
- Improved windows
Within eQUEST, the default HVAC system used to transfer heat from one zone to another is a water-loop heat pump. However, there are three components in the water loop heat pump that are not part of a VRF system: a condenser water loop, boilers, and cooling towers. In lieu of using a water loop heat pump method, we selected single zone split system heat pumps. A VRF system is essentially a group of air-to-air heat pumps that are allowed to exchange energy between one another before the outdoor heat pump is required to extract or add energy back into the system. An exceptional calculation was provided using the eQUEST modeling outputs to define the energy savings associated with the zonal heat exchange.
ENERGY USE VERIFICATION: $0.81/SQ FT/YR
After one year of operation, we found the energy use results between the modeled data and the measured data were very similar (Figure 1). Although efficiency measure energy savings information is unavailable in Figure 1, both gas and electric utility data is included, and show that the methods implored in the energy model provide exacting results.The 82,800-sq-ft LEED Platinum rated building utilized 827,456 kWh/yr and 1,763 therms/yr in its first year of occupancy for an energy-usage intensity (EUI) of 36 kBtu/sq ft/yr. The building used less energy than predicted, but not by much, with an energy model EUI of 38 kBtu/sq ft/yr.
The annual energy costs for the designed building were $0.83/sq ft/yr, where the actual energy costs for the building are $0.81/sq ft/yr.
LEED CREDITS ACHIEVED
USGBC gave the maximum 10 points for EAc1 energy savings to the project; this was easily obtained using the combination DOAS and VRF systems. However, to satisfy EAc4, the team had a more difficult task to limit the amount of refrigerant on a per-ton basis. With the inclusion of the DOAS, the overall building refrigerant budget was reduced to meet the credit requirement along with the prerequisite of zero CFC-based refrigerants. The VRF system allowed the building to easily split into five different tenant zones that aided EAc5 measurement and verification.In addition to the mechanical-related credits, LEED points were also awarded for the recycled content where the project team reused 75% of the existing Packer-Scott Building; 75% of the construction waste was recycled; a green roof was constructed; and bioswales treated stormwater runoff. The planned PV array has a structural system installed above the green roof to maintain a cool array for more efficient performance.
THE ECONOMIC CASE FOR SUSTAINABILITY
The Mercy Corps building is the physical representation of the organization’s core values - participation, accountability, and peaceful change. These values - along with the systems, design, construction - developed a responsible building in the end. Detailed energy modeling became an essential tool in defining the design path, especially regarding which efficiency measures were applied. The energy model precision was verified by the actual energy cost of the Mercy Corps building, further strengthening the economic case for sustainability.ESNew Headquarters Building: Metaphor for Community Caring and Sustainability
Mercy Corps is a non-profit international disaster relief and economic development organization serving under-developed societies worldwide to alleviate suffering and poverty. Its world headquarters embodies its sustainable, community-focused approach to global action. The headquarters also brings new life to an economically challenged neighborhood in Portland, OR. It revitalizes an existing historic building and makes an addition that is sensitive to the character and patterns of Portland’s Old Town.The existing 1878 building was repaired and restored to its original form. The new addition respects the historic pattern of the four-story, quarter-block development and is complimentary to the composition, scale, and materiality of the existing building while also being frankly modern.
Mercy Corps’ culture recognizes that individuals gain strength through interaction and cooperation. The value of teamwork is reflected in the metaphors of the crucible and weaving apparent in both the interior and exterior of the building.
The interior plan is organized around a very dynamic open space, a light-filled crucible holding a multi-directional staircase that connects people in all quadrants of the building and creates opportunity for informal collaboration. On the exterior, a series of woven patterns of terra cotta and glass symbolize the interactive nature of Mercy Corps’ work with people of the developing world.
Social equity is a core principle of Mercy Corps. The building’s plan gives the best views, daylight, and fresh air to the most people by locating open offices at the perimeter of the existing building and on the eastern façade in the new building with views of the park, river and distant mountains.
Sustainability is central to Mercy Corps’ mission. Its new home is a model for how to build responsibly and achieved a Platinum LEED® certification, the highest level of sustainable certification recognized by the USGBC. At the building’s opening, USGBC President, Rick Fedrizzi, stated, “This project is what LEED Platinum should be all about. It will be a beacon.”
By inspiring collaboration, honoring context, and embracing innovation, this building embodies the core values of a progressive organization addressing the most pressing problems facing the world today.
